Cyclosporin A (CsA), a neutral cyclic undecapeptide isolated from the fungus Tolypocladium injlaturn and currently marketed as Neoral and sandimmunem (Novartis, Basel, Switzerland), has been widely used for the prevention of organ transplant rejection.
The molecular basis for the immunosuppressant activity of cyclosporin A and cyclosporin analogues begins with the passive diffusion of the cyclosporin (Cs) molecule into the cell, followed by binding to its intracellular receptor, cyclophilin A (CypA). CypA belongs to a family of proteins that catalyze cis-trans peptidyl-prolyl isomerization, i.e., PPIase, a rate-limiting step in protein folding. CsA and other cyclosporin analogues bind to the active site of CypA. However, immunosuppression is not believed to be due to the inhibition of CypA PPIase activity. The target of the CsA-CypA complex is a Ca2+-calmodulin-dependent serine-threonine-specific protein phosphatase, calcineurin. In T-cells responding to antigen presentation, an increase in intracellular Ca2+ activates calcineurin, which subsequently dephosphorylates the transcription factor called the nuclear factor of activated T-cells (“NFAT”). Dephosphorylated NFAT undergoes a molecular change, e.g., homodimerization that allows it to cross into the nucleus, and promotes the expression of T-cell activation genes. CsA and other immunosuppressive cyclosporin derivatives inhibit calcineurin which results in the inhibition of expression of cytokine genes, e.g., interleukin-2 (IL-2) that promotes T-cell activation and proliferation, i.e., immunosuppressive activity.
Since the original discovery of Cyclosporin, a wide variety of naturally occurring cyclosporins have been isolated and identified, and many further normatural cyclosporins have been prepared by total- or semi-synthetic means or by the application of modified culture techniques. The class comprised by the cyclosporins is thus now substantial and includes, for example, the naturally occurring cyclosporins A through Z [cf., Traber et al.; 1, Hely. Chim. Acta, 60, 1247-1255 (1977); Traber et al.; 2, Helv. Chim. Acta, 65, 1655-1667 (1982); Kobel et al.; Europ. J. Applied Microbiology and Biotechnology, 14, 273-240 (1982); and von Wartburg et al.; Progress in Allergy, 38, 28-45 (1986)], as well as various non-natural cyclosporin derivatives and artificial or synthetic cyclosporin derivatives and artificial or synthetic cyclosporins including dihydrocyclosporins [in which the—MeBmt—residue is saturated by hydrogenation]; derivatized cyclosporins (e.g., in which the 3′-O-atom of the —MeBmt—residue is acylated or a further substituent is introduced at the a-carbon atom of the sarcosyl residue at the 3-position); and cyclosporins in which variant amino acids are incorporated at specific positions within the peptide sequence, e.g. employing the total synthetic method for the production of cyclosporins developed by R. Wenger—see e.g. Traber et al., 1; Traber et al., 2; and Kobel et al., loc cit. U.S. Pat. Nos. 4,108,985, 4,220,641, 4,288,431, 4,554,351, 4,396,542 and 4,798,823; European Patent Publication Nos. 34,567A, 56,782A, 300,784A and 300,785; International Patent Publication No. WO 86/02080 and UK Patent Publication Nos. 2,206,119 and 2,207,678; Wenger 1, Transpl. Proc., 15 Suppl. 1:2230 (1983); Wenger 2, Angew. Chem. Int. Ed. 24 77 (1985) and Wenger 3, Progress in the Chemistry of Organic Natural Products, 50, 123 (1986). Several synthetic modifications of the —MeBmt—residue residing at position 1 of the cyclosporin undecapeptide have been described including: Park et al., Tetrahedron Lett. 1989, 30, 4215-4218; U.S. Pat. Nos. 5,239,037, 5,293,057; U.S. Publication Nos. US20020142946, US20030087813, and US20030104992 assigned to Enanta Pharmaceuticals, Inc.; PCT Publication Nos. WO99/18120 and WO03/033526 both assigned to Isotechnika; and U.S. Pat. Nos. 4,384,996, 4,771,122, 5,284,826, and 5,525,590 assigned to Sandoz.
The compound cyclosporin (cyclosporin A or CsA) has found wide use since its introduction in the fields of organ transplantation and immunomodulation, and has brought about a significant increase in the success rate for transplantation procedures. Undesired side effects associated with cyclosporine, however, such as nephrotoxicity, have led to a continued search for immunosuppressant compounds having improved, efficacy and safety. Side effects with systemic CsA include increase in diastolic blood pressure and decrease in renal function. Other side effects include hepatic dysfunction, hypertrichosis, tremor, gingival hyperplasia and paraesthsia. The systemic toxicity of CsA limits its use for the treatment of certain diseases. Accordingly, a need exists for compounds which exhibit immunosuppressive activity while not producing systemic toxicity.
Cyclosporin A and certain derivatives have been reported as having anti-HCV activity, see Watashi et al., Hepatology, 2003, Volume 38, pp 1282-1288, Nakagawa et al., Biochem. Biophys. Res. Commun. 2004, Volume 3 13, pp 42-7, and Shimotohno and K. Watashi, 2004
American Transplant Congress, Abstract No. 648 (American Journal of Transplantation 2004, Volume 4, Issue s8, Pages 1-653). The authors of the Nakagawa et al. paper state that certain chaperone activities, such as those of cyclophilins, may be crucial for the processing and maturation of the viral proteins and for viral replication. Cyclosporin derivatives having HCV activity are known from International Publication Nos. WO2005/021028, WO2006/039668, WO2006/038088, WO 2006/039688, WO 2007/112352, WO 2007/112357, WO 2007/112345 and WO 2007/041631.
A subsequent controlled clinical trial showed that a combination of cyclosporin A with interferon α2b is more effective than interferon monotherapy, especially in patients with high viral loads (Inoue et al., “Combined Interferon α2b nd Cyclosporin A in the Treatment of Chronic Hepatitis C: Controlled Trial,” J. Gastroenterol. 38:567-572 (2003)).
PCT International Patent Publication No. WO 2006/005610 recently described the use of a combination of cyclosporin A and pegylated interferon for treating hepatitis C viral infection. In addition, PCT International Patent Publication No. WO 2005/021028 relates to the use of non-immunosuppressive cyclosporine for treatment of HCV disorders. Also, Paeshuyse et al., “Potent and Selective Inhibition of Hepatitis C Virus Replication by the Non-Immunosuppressive Cyclosporin Analogue DEBIO-025,” Antiviral Research 65(3):A41 (2005) recently published results for a non-immunosuppressive cyclosporin analogue, DEBIO-025, that exhibited potent and selective inhibition of hepatitis C virus replication. Debio-025 does possess potent binding affinity for cyclophilin A.